The present invention pertains to solid-shell centrifuges for separating solids from liquids that include a scroll for conveying the extracted solids out of the centrifuge and structure for supporting the scroll within the bowl shell. The invention particularly pertains to the drive means for selectively driving the scroll conveyor at a slightly different speed than the bowl shell during the solids conveying process while the centrifuge continues to operate.
Some centrifuges used to separate solid materials out of a stream of liquid are operated on an intermittent basis. After some period of operation with a stream of liquid passing through the centrifuge, the flow of liquid is terminated and the centrifuge stopped so that the separated solids can be removed from the centrifuge bowl. While such batch processing of some fluids is satisfactory, in many manufacturing situations, a continuous separation process is desired so that the flow of liquid does not have to be periodically terminated.
Centrifuges of the type having a helical conveying scroll mounted within a frustoconical centrifuge bowl are commonly employed to separate solids from liquids on a continuous or semi-continuous basis. Typically, a liquid-solid mixture or slurry is continuously introduced into the centrifuge, and occasionally or even continuously a rotary speed differential is established between the rotating bowl and the scroll so that the scroll can convey the separated solids out one end of the centrifuge bowl at the same time as separated liquid flows out the other end of the bowl. A wide variety of apparatus have been employed to attempt to achieve the speed differential between the scroll and bowl with varying success and reliability. The speed differential apparatus tends to be a relatively high maintenance item as compared to the remainder of the centrifuge. Examples of prior art speed differential apparatus are to be found in U.S. Pat. Nos. 4,129,249; 4,228,949; and 5,529,566.
An object of the present invention is to provide a centrifuge with a highly reliable speed differential drive apparatus for precessing the scroll slightly faster than the bowl shell on either a continuous or occasional basis to extract separated solids from the bowl while the centrifuge continues to separate solids from a stream of liquid. Another object of the present invention is to process the stream of liquid more effectively by providing means for accelerating the liquid as it is introduced which smoothly delivers the newly introduced liquid to the region of the maximum operating fluid level within the bowl as an essentially laminar flow.